1. Field of the Invention
The present invention relates to a liquid crystal display (LCD), and more particularly, to a method for fabricating an LCD having a liquid crystal dropping method applied thereto.
2. Background of the Related Art
Keeping pace with development of an information oriented society, demands on displays increase gradually in a variety of forms, and, recently to meet the demands, different flat display panels, such as LCD (Liquid Crystal Display), PDP (Plasma Display Panel), ELD (Electro Luminescent Display), VFD (Vacuum Fluorescent Display), and the like, have been under development, and some of which are employed as displays in various apparatuses.
The LCDs have been used most widely as mobile displays while the LCDs replaces the CRT (Cathode Ray Tube) owing to features and advantages of excellent picture quality, lightweight, thin, and low power consumption. Besides the mobile type LCDs, such as a monitor of a notebook computer, the LCDs are under development for televisions (TVs) for receiving and displaying broadcasting signals, and computer monitors.
Despite the various technical developments in the LCD for serving as a display in different fields, the studies for enhancing a picture quality of the LCD as a display are inconsistent as to the features and advantages of the LCD in many aspects. Therefore, for employing the LCD in various fields as a general display, the key for development of the LCD lies on whether the LCD can implement a high quality picture, such as a high definition, a high luminance, and a large sized screen while the LCD has a light weight, thin, and a low power consumption.
The LCD is provided with a liquid crystal display panel for displaying a picture, and a driving part for providing a driving signal to the liquid crystal display panel, wherein the liquid crystal display panel has first and second glass substrates bonded together with a gap between the substrates, and a liquid crystal layer injected between the first and second glass substrates.
On the first glass substrate (a TFT array substrate), there are a plurality of gate lines arranged in one direction at fixed intervals, a plurality of data lines arranged in a direction perpendicular to the gate lines at fixed intervals, a plurality of pixel electrodes in respective pixel regions defined at crossing points of the gate lines and the data lines to form a matrix, a plurality of thin film transistors switchable in response to a signal from the gate lines for transmission of a signal from the data line to the pixel electrodes.
The second glass substrate (a color filter substrate) has a black matrix layer for shielding light from parts excluding the pixel regions, a red, green, blue (R, G, B) color filter layer for displaying colors, and a common electrode for implementing a picture.
The foregoing first and second substrates are bonded together, spaced by spacers, with sealant having a liquid crystal injection opening therein, through which liquid crystal is injected.
The liquid crystal is injected by evacuating the space between the two bonded substrates and dipping the liquid crystal injection opening in liquid crystal. The liquid crystal flows in the space between the two substrates by the capillary tube phenomenon. Once the liquid crystal is injected, the liquid crystal injection opening is sealed by the seal.
However, the related art method for fabricating an LCD having the liquid crystal injection method applied thereto has the following problems.
First, the related art method has poor productivity because the dipping of the liquid crystal injection opening in a liquid crystal while the space between the two substrates are maintained at a vacuum for injection of the liquid crystal, takes a long time.
Second, the liquid crystal injection, particularly, into a large sized LCD, is liable to cause imperfect filling of the liquid crystal in the panel, which is a cause of a defective panel.
Third, the complicated and lengthy time of the fabrication process results in requiring many liquid crystal injection devices, that occupy a lot of space.
Accordingly, a method for fabricating an LCD by using a liquid crystal dropping method has been researched. A Japanese laid-open patent publication No. 2000-147528 discloses the following liquid crystal dropping method.
A related art method for fabricating an LCD having the foregoing liquid crystal dropping method applied thereto will be explained. FIGS. 1A-1F illustrate the steps of a related art method for fabricating an LCD.
Referring to FIG. 1A, ultraviolet (UV) sealant 1 is coated on a first glass substrate 3 having a thin film transistor array formed thereon to a thickness of approx. 30 μm, and liquid crystal 2 is dropped on an inner side of the seals 1 (a thin film transistor array part). No liquid crystal injection opening is provided in the seal 3.
The first glass substrate 3 is mounted on a table 4 in a vacuum container ‘C’ which is movable in a horizontal direction, and held by a first suction device 5 holding an entire bottom surface of the first glass substrate 3 by vacuum.
Referring to FIG. 1B, an entire bottom surface of the second glass substrate 6 having the color filter array formed thereon is held by a second suction device 7 by vacuum, and the vacuum container ‘C’ is closed and evacuated. The second suction device 7 is moved downward in a vertical direction until a gap between the first and second glass substrates 3 and 6 becomes 1 mm, and the table 4 with the first glass substrate 3 thereon is moved in a horizontal direction, to pre-align the first and second glass substrates 3 and 6.
Referring to FIG. 1C, the second suction device 7 is moved downward until the second glass substrate 6 comes into contact with the liquid crystal 2 or the seal 1.
Referring to FIG. 1D, the table 4 with the first glass substrate 3 thereon is moved in a horizontal direction to align the first and second glass substrates 3 and 6.
Referring to FIG. 1E, the second suction device 7 is moved downward until the second glass substrate 6 comes into contact with the seals 1, and is pressed downward until a gap between the second glass substrate 6 and the first glass substrate 3 becomes 5 μm.
Referring to FIG. 1F, the bonded first and second glass substrates 3 and 6 are taken out of the vacuum container ‘C’, a UV beam is directed towards the seal 1, to set the seal 1, thereby finishing fabrication of the LCD. In the seal 1, there are main seals and dummy seals surrounding an active region of the LCD.
However, the foregoing related art method for fabricating an LCD having the liquid crystal dropping method applied thereto has the following problems.
First, the sealant coating and liquid crystal dropping on the same substrate requires a long fabrication time period before the two substrates are bonded.
Second, as the sealant is coated and the liquid crystal is dropped on the first substrate while no progress is made for the second substrate, there is an unbalance of a fabrication process between the first and second substrates, which implies an ineffective operation of the production line.
Third, because the sealant is coated and the liquid crystal is dropped on the first substrate, the first substrate with a coat of the sealant applied thereto cannot be cleaned by an ultra sonic cleaner (USC). Therefore, as the sealant that is to bond the two substrates should not be washed away, particles cannot be removed, which may cause defective contact of the sealant during bonding.
Fourth, the movement of bonded substrates yet to be set for venting, or for unloading after the venting, is liable to cause misalignment as a size of the substrate increases.
Fifth, it is difficult to maintain a bonded state in subsequent steps until the sealant is set as the size of the substrate increases.
Sixth, the movement of the liquid crystal between the substrates caused by the misalignment of the substrates causes defective orientation of the liquid crystal.
Seventh, the misalignment of the substrates deteriorates the aperture ratio.
Eighth, the defective orientation of the liquid crystal is liable to cause blots like scratches, and blots related to a luminance.
Ninth, the bonding of the two substrates only by a physical force of the table and the second suction device may cause defective bonding due to non-uniform application of pressure throughout the substrate in a case where levels of the table and the second suction device are not correct.
Tenth, the introduction of air into the vacuum container for restoring the vacuum container into atmospheric pressure after the bonding may deteriorate a state of the vacuum container due to moisture contained in the air.